In any county which has safety members as defined in Sections 31470.2 and 31470.4 subject, prior to January 1, 1962, to the provisions of this article, the board of supervisors may adopt the provisions of this section.

The retirement allowance for any safety member subject to this article for service rendered prior to the date of adoption of this article by a county board of supervisors shall be computed in accordance with the provisions of Section 31664. The retirement allowance of any such member, subject to this article, with respect to service performed after the effective date of adoption by the county of this article shall equal the total of the following:

The retirement allowance for any safety member who is not subject to this article shall be computed in accordance with the provisions of Section 31664.

Any member who becomes a safety member after the adoption date of this section shall be subject to the provisions of this article.

This section shall not apply to any safety member who is a member on date of adoption of this section unless within 60 days thereafter he files with the board a signed written statement expressing his desire to have the section apply to him.

Any member subject to the provisions of this section may elect deferred retirement pursuant to Article 9 (commencing with Section 31700) of this chapter.